Oric 1 and Atmos - repair help needed - EDIT: Oric 1 works

[YuT666]

Hi,

got two defective Orics (1 and an Atmos) and both show bad screens. It looks like a defective cpu and/or ULA problems.

So i'm searching for someone, who had similar problems and tried to repair it.



The reset pins (pin 40) are showing "low" (1 second) and then "high" (so this should be good). All ram chips are only warm, none of them is hot (both computers).

1. Oric 1:



2. Atmos:



Thanks in advance.

Regards

Tom

[Chema]

Hi!

I'm not a hardware guy, but I'd say the screens correctly show the ram pattern prior booting the rom. So probably the ULA is ok, which is great. I had a similar issue when trying to boot my Oric after 20 years or so, and I ended up hitting it in dispair against the table (softly). Then it booted.

I don't think it got scared, so probably there was a bad contact with the rom chip (which is socketed). I would start there.

In any case there are plenty of hardware experts in the forum who will p of ably give much better help.

Happy new year!

[YuT666]

Hi,

i forgot to mention, that i already removed the rom chips and cleaned the pins. Nothing changed.

But ... thanks for your answer, i really appreciate it.

Happy new year too!

[Dbug]

If you have possibility to burn eproms, you could try the Oric diagnostic rom:
http://oric.signal11.org.uk/html/diagrom.htm

Basically it goes through the hardware step by step trying to see what's working or not.

This diagnostic ROM is designed to quickly prove out an Oric/Atmos 48K mainboard hardware. When
used in an ORIC it replaces the system ROM with simpler firmware to allow step by step testing of the
RAM, ULA, VIA, PSG (Sound Chip) and associated hardware. Where the ORIC system ROM may
hang due to a problem at initialization, this ROM should give some idea of where the fault may lie.
If the 8912 (PSG) or 6522 (VIA) chip is not installed, a RAM test and ULA test is performed at the
very least. A full test takes under 2 minutes if all steps pass. Even with the ULA missing, an external
1MHz clock can be provided to check the basic CPU access to ROM.
A keyboard is not required to be fitted for these tests, user input is via the NMI (reset) button. This is
because successful use of the keyboard relies on the ULA, VIA, PSG being in working condition,
which cannot be assumed! Also, for repair and diagnostics, the keyboard is often disconnected.

[YuT666]

Yes, i know this page and the diagnostic rom, but i don't have a eprom burner. Maybe it's time to buy one ...

[Chema]

Maybe a stupid question, but as both Oric seem to have a similar problem (which is surprising) are you sure you are using the correct PSU? Polarity seems right, as both try to boot, but if I remember correctly they needed 9v 600mA. 7.5v might do too, but I never tried.

[iss]

Chema was faster than me. On eBay these Oric's were announced without PSU, so really what is your power adapter?
Can you check the 7905 output voltage? Btw, the story of your Oric's actually starts in the other forum.
You can try to ask the seller if he recall any details why computers don't work.

[YuT666]

Well, i bought these the two Orics on ebay and got a huge refund, so i really spent only a handful of bucks for them. I think, that i should try to repair this beautiful minis.

I'll check the 7905 voltages soon.

And no Chema, it's not a stupid question ... all your help is welcome.

@All:

One of the power supplies i tried is this one:

http://www.leicke.eu/de/products/NT03092

9V with 2A. This should be a good one.

I tried to shorten the pins 1 and 40 of the cpu, but all i got is a minimal different noise. The Orics wants to reset, but the screen is always the same.

And yes, the ULA should be ok and i hope the 6502A CPU works too.

Hm ... maybe it is the 6522 VIA.

I bought a Saleae Logic Analyzer and i'm still waiting for the clamps. But i don't know anything about measuring with this Saleae thing.

Another question ... is it possible to "piggy back" an other 6502 over the old one?

[iss]

Yes, this PSU should be ok. You can check here for schematics and info, especially Oric Service Manual.
In the service manual is described how to search faulty chips, but I don't recommend cutting tracks, it's too cruel .
You can always manually check tracks and pin connections using schematics and Ohm-meter (buzzer).
The logic analyzer will help too - working with it is not difficult but fun.

[YuT666]

Great forum ...

I think, i'll need some time to get into that Oric thing. Would be great, if i could repair them before i die ... ... repaired some Thomsons, BBCs and Amstrads in the past, but i'm not so much into that ohmmeter and LA stuff.

Anyway ... i think your Oric Service Manual link will be a good help.

[YuT666]

The Oric Service Manual is good, but there are no pcb modifications listed there. Only the numbers and there are no modification leaflets included.

I need some info about the 63b mid of IC21.

Because:

One thing to check is that modification 63b on IC21 has been implemented. If not, this can result in initialization faults ...

Some more special infos about the modifications would be great anyway.

Here is solder side of the Issue 3 Board.

[iss]

It's on page 72 - noted as 63 (b) .
But before cutting tracks, you can try to short the pins of the capacitor C21 with metal tweezers for 1 second - this will reset the CPU.

[YuT666]

Great, i should check my eyes ... i'm getting old.

Thanks.

EDIT: Don't know how what to do first ... i checked the 7905 and the voltages are ok. It suckes, 'cause shortening the reset pin only shows some noise.

A question ... should the ULA be cold, warm or hot after some minutes?

[YuT666]

Received an EPROM with the Oric diagnostic tool (http://oric.signal11.org.uk/html/diagrom.htm - it worked in a working Oric), plugged it in, but no change ... i only received the same pattern and no diagnostic things. Crap ... i'll throw them in the bin!

[Chema]

Still the squared pattern in the screen? In my opinion the processor is not booting. It could be many things, including the VIA, but every time I saw a VIA failing the symptoms were strange behaviors, hangs, etc.

What you experience is the typical situation where a PSU is not providing enough power. Because it is a notable coincidence that both fail exactly in the same way. But I assume you checked the voltage out of the regulator with the Oric on, and it was OK. I also assume you plug the PSU and then the plug into the Oric.

Did you check the main ICs are getting 5volts?

I don't know how to test if there is any component in the board or any cut track which may be causing trouble, but changing the 6502 could be a good idea. Again it is quite strange that both CPUs fail exactly the same.

Sorry for not being able to help any further...

Good luck!